This invention relates generally to fuel level sensors and, more particularly, to fuel level sensors for use with recreational vehicle fuel tanks, such as those found on snowmobiles, personal watercraft, and motorcycles.
Numerous design constraints are imposed upon fuel level sensors, particularly fuel level sensors for use with recreational vehicles. For instance, fuel level sensors must be capable of withstanding corrosive environments, as the sensor is at least partially submerged in fuel and various types of fuel additives throughout its operational life. Also, the sensor is frequently subjected to extreme vibration and shock, elements that are intensified in recreational vehicle applications, particularly those using two-stroke engines. In addition to these requirements, it is desirable that the sensor be of relatively low cost, compact in size, and fairly easy to manufacture and package. Traditionally, two primary fuel level sensor designs have been employed to address the aforementioned needs. The first entails a purely mechanical design while the second utilizes magnetically activated reed-switches.
The purely mechanical fuel level sensor generally includes a float, a spiral strip of metal, and a fuel gauge. In operation, the float moves according to the fuel level in a vertical direction along the spiral strip of metal, which is attached to an indication needle of the fuel gauge. As the fuel level rises and lowers, the float causes the strip of metal to turn, thus moving the indication needle of the fuel gauge and informing the operator of the current fuel level.
The reed-switch type fuel level sensor, on the other hand, typically includes an elongated circuit board containing a series of reed-switches and resistors and is encapsulated by a protective housing that is partially surrounded by a float having a magnetic component. The encapsulated circuit board is generally aligned in a vertical orientation, such that a change in the fuel level causes the float to move up and down along the circuit. As the magnet carrying float vertically moves along the circuit, reed-switches located at various vertical positions are activated and deactivated. Interspersed between these reed-switches are resistors, all of which are connected in series and help form a complete current path. When the fuel level is at a half of a tank, for example, the magnet carried by the float activates a reed-switch located at an equivalent vertical position. Activating that reed-switch causes the resistors located below the switch to be shorted. Therefore, assuming a constant voltage source, the amount of electrical current through the circuit is related to the number of series connected resistors that it flows through, and thus is related to the fuel level. Numerous fuel level sensors employ a magnet carrying float and reed-switches, including the sensors disclosed in U.S. Pat. Nos. 4,976,146 and 4,384,184.
The ""146 patent discloses a reed-switch style liquid level sensor having a plurality of reed switches that are overlapping, vertically spaced apart, and are slightly inclined to the vertical axis. A digital driver circuit is connected to each reed-switch and an electrical readout is connected to each digital driver such that the readout expresses the current liquid level within a resolution corresponding to half the distance between spaced apart reed-switches. Though the sensor seen in the ""146 patent utilizes reed-switches for determining liquid levels, that design does not disclose the use of series connected resistors nor non-overlapping reed-switches.
The fuel level sensor seen in the ""184 patent reduces the number of reed-switches by utilizing a non-overlapping reed-switch configuration. The reed-switches of this design are laid out in a vertical, non-overlapping orientation and are wired in a generally parallel manner. Activation of one of the reed-switches does not short resistors further down the circuit board, as described above. Rather, each reed-switch is electrically connected to a terminal such that activation of one of the reed-switches connects the appropriate terminal to power, thereby driving an indicator lamp or some other type of electrical device. The reed-switches are encapsulated in a first tube filled with a spark suppressing inert gas, the tube is then surrounded with a dielectric oil, and the entire device is enclosed in a second protective tube.
Thus, it would be advantageous to provide a fuel level sensor that utilized series connected resistors and magnetically activated switches in order to provide an accurate, compact, and rugged fuel level sensor.
In accordance with the present invention, there is provided a fuel level sensor for use in a vehicle fuel tank that comprises an electrical circuit, an elongated housing surrounding the electrical circuit, and a float assembly. The electrical circuit is elongated, extends in a vertical direction, and has a plurality of series connected resistors and a plurality of magnetically activated switches. The switches are located at various axial positions along the electrical circuit and are connected between two of the resistors at one end and a common node at the other end. The float assembly includes at least one magnet and surrounds a segment of the housing such that the float assembly is capable of freely rotating about the housing and vertically moving along the housing according to the fuel level in the fuel tank. Further, the magnet(s) is oriented such that it is capable of activating each of the switches from any angular orientation of the float assembly relative to the housing.
In accordance with another aspect of the present invention, there is provided a fuel level monitoring system for use in a vehicle that comprises a battery, a vehicle fuel tank, a fuel level sensor, and a fuel gauge. The fuel level sensor is located within the fuel tank, is coupled to the battery such that it receives a first signal, and comprises an elongated electrical circuit, an elongated housing surrounding the circuit, and a float assembly. The electrical circuit extends in a vertical direction and has a plurality of series connected resistors and a plurality of magnetically activated switches. The switches are located at various axial positions along the electrical circuit and are connected between two of the resistors at one end and a common node at the other end. The float assembly includes at least one magnet and surrounds a segment of the housing and is freely rotateable about the housing such that the magnet(s) is capable of activating each of the switches from any angular orientation of the float assembly relative to the circuit. Also, the float assembly is vertically moveable along the housing according to the fuel level in the fuel tank. The fuel level sensor utilizes the first signal to produce a second signal representative of the fuel level, and the fuel gauge is coupled to the fuel level sensor for receiving the second signal. Thus, the fuel gauge is capable of utilizing the second signal to inform an operator of the fuel level.
Objects, features, and advantages of this invention include providing a fuel level sensor that utilizes a freely rotatable, magnet carrying float assembly to activate reed-switches located at various axial positions along an elongated circuit such that activation of the switches is independent of the angular orientation of the float assembly with respect to the circuit, wherein the fuel level sensor is compact in size, is of a rugged design for use in recreational vehicle applications, and is of relatively simple design, economical manufacture and assembly and has a long and useful life in service.